In the previous paragraph we discussed if Simlox is a tool whereby Inventri can be simulated. If Inventri could be simulated, the assumption could be made that Simlox is a good simulation software and that the Simlox model is programmed correctly. In this chapter we investigate the differences between mission availability and the operational availability of Inventri. Before the comparison between the mission and operational availability can be made, an availability study has to be conducted to identify the worst case scenario in terms of mission profile and mission deployment. The worst case scenario of the mission intensity is that the ships are deployed in which the average mission availability is at its lowest. The study to this worst case scenario is discussed in section 6.2.1. Afterwards a comparison is made between the mission availability and the operational availability.
6.2.1
Mission intensity
The worst case towards mission availability among missions is assumed to be the deployment of two mission ships at the same time. This seems logical, because that the demand of parts failure will start at the same moment. The two ships create a demand at the same time. The best case scenario will probably be that the mission ships are deployed consecutive to each other during the year. For example: Mission ship one deploys in the first half year and the second mission ship deploys in the second half year. The short-mission ship will be deployed around mission ship one and two.
What the intensity of the missions are studied by changing the deployment of the ships. Mission intensity is studied by an experiment in which the mission profiles are modified weekly. One mission ship (mission ship 1) and the short-mission ship are unmodified. The other mission ship (mission ship 2) is modified. This second mission ship (mission ship 2) is deployed at Week 0, 1, 2 …, or 30. For the
44 Case Study The transition from operational availability to mission availability J.L. Schmal overview see appendix G. For this experiment we will also use the product structure of Figure 7 in section 2.1.1, supply chain of Figure 10 in section 3.2.3.
Figure 18 shows where the mission availability is displayed in respect of the mission deployment. The vertical axis is the mission availability and the horizontal axis is the deployment week of the second mission ship. Like it was assumed the availability is higher when the mission ships are deployed consecutive to each other.
Figure 18: Mission availability differences per ship
Note that the mission availability of the second ship is consequently lower until week 22. This seems quite logical; the spare parts are ordered on a first-come-first-serve basis. The failed parts which are ordered first will be handled first. Logically this will be mission ship 1. The first mission ships creates a demand from t = 0 and the second ship from t > 0.
The short-mission ship will have high mission availability. The short-mission ship will sail multiple missions during a year with a mission duration from 3 to 7 days. In this case the chance a part fails is much smaller, because of the small mission durations.
The total difference among the average mission availabilities of three ships in respect to deployment of the second mission ship is displayed in Figure 19. The vertical axis is the average mission availability; the average mission availability of three ships. The horizontal axis is the deployment week of the second mission ship. The difference will increase up to more than 2%. These differences are created using the scenario with two mission ships and a short-mission ship. When the mission ships have larger or smaller mission lengths, then the difference will probably change in accordance with the mission length.
70.00% 75.00% 80.00% 85.00% 90.00% 95.00%
J.L. Schmal The transition from operational availability to mission availability Case Study 45 Figure 19: Differences in average mission availability
We can assume that the mission intensity is the highest when two mission ships deploys at the same time. The worst case scenario is used in this research, because Thales aims to have penalties as little as possible, because penalties could create high costs over a very short period of time. By using the worst case scenario the chance in having penalties will be reduced, because in general the ships will not be deployed at the same time.
6.2.2
Comparison between mission and operational availability
The missions are implemented within Simlox following the sequel of Table 5 in section 3.2.3. The simulation run is 5 years with one year warm-up period using 25000 replications. For this experiment we will use the product structure of Figure 7 in section 2.1.1, supply chain of Figure 10 in section 3.2.3, the time parameters: repair lead-time 14 days & return shipment of 21 days and worst case ship deployment of Figure 18 in section 6.2.1. The results are plotted in Figure 20. The vertical axis is the average availability of three ships per year. (
3
3 2 1 ship ship shipA
A
A
This is the operational or the mission availability. The horizontal is the costs of the spare parts.
Figure 20: Difference between operational availability and mission availability
79.50% 80.00% 80.50% 81.00% 81.50% 82.00% 82.50% 83.00% 83.50% 84.00% Avera ge mis sion ava ila bility 0% 20% 40% 60% 80% 100% Avera ge ava ila bility
46 Case Study The transition from operational availability to mission availability J.L. Schmal Using the mission implementation a comparison could be made between operational availability (Inventri) and the average mission availability (Simlox).
The average operational availability of three ships is calculated when using Inventri. Again, multiple ships are used and again the average is calculated of three ships. Despite the two mission ships and the short-mission ship, the differences between Inventri availability and mission availability is approximately 13% for the 21 days return shipment and a repair lead-time of 14 days. The other scenarios are simulated in the same way. No significant differences were found.
There is a big difference between mission profiles and the Inventri calculation. Inventri calculates the supply availability. This means that the calculation is done in a steady state. The supply availability is also taken into account when the ship is in the harbor and the system is not operational. The spare parts supply for the ships are available during a large part of a year when the ship is in the harbor. The mission availability only takes the spare parts supply availability into account when the ship is on a mission. The measurement period of the mission availability is therefore much shorter than the supply availability when calculated using Inventri. Figure 21 gives better overview.
Figure 21: Example measurement 4 months mission availability in respect to operational availability
If Thales uses the spare parts provisioning based on Inventri than Thales will get penalties. With a mission availability target set at 93.3% Thales will not be able to reach this level of availability. For this reason Thales has to calculate the mission availabilities with the software Simlox.